Are you keeping your iPhone connected to a charger for a long time or while sleeping, because you want it to be fully charged when you wake up??
Well, if your iPhone is fully charged for too long, it can damage the battery of your device.
While OBC is on, the iPhone will charge slower, reducing the amount of time it spends fully charged and plugged in.
To prevent your battery health Apple's “Optimized Battery Charging” feature comes in.
Optimized Battery Charging (OBC) is a feature that stops your iPhone from charging in order to protect its battery health
It might sound like a bad thing but it is a great feature.
This keeps your device’s battery healthy, and makes every charge last longer.
If you don't like it, or want to charge your device fast when you're in a hurry, you can easily turn Optimized Battery Charging on or off in the setting section of the device.